In household, commercial, industrial or institutional warewashing or dishwashing commonly available dishwashing machines have mechanical spray mechanisms in which ware are sprayed first with a cleaning solution and second with a rinsing solution. This functional design is substantially different than the design of a household laundry machine in which objects to be cleaned are immersed in a cleaning medium. Typically, in spray washers both the cleaning solutions and rinsing solutions are held in a machine reservoir, pumped to a spray mechanism where the cleaning or rinsing solution is directed under pressure onto the ware, and after cleaning or rinsing the solution returns to the reservoir. Such spray mechanical washers can operate with a variety of combinations of cleaning, rinsing and other steps. However most machines operate with one or more steps of the following sequence: scraping, rinsing, washing, rinsing, and sanitizing. Commonly machines are classified by the temperature of their cleaning and rinsing. High temperature machines use thermal energy to achieve a sanitizing action while low temperature machines use chemical sanitizing agents. In high temperature machines a minimum of two operations are required. The ware is contacted at high temperature (140.degree.-180.degree. F.) with an alkaline low foaming cleaner solution and are then rinsed with water at a sanitizing temperature which contains a rinse aid to promote drying with a minimum of spotting or filming. In low temperature machines, the ware are contacted with hot tap water containing an alkaline low foaming cleaner solution and are then rinsed with hot tap water (120.degree.-140.degree. F.) which contains a rinse agent and are contacted with an active halogen composition to achieve acceptable sanitization. The concentration of active halogen required to achieve effective sanitization typically falls within the range of about 50-100 parts of available halogen or chlorine per million parts of the rinse composition.
Typically, alkaline cleaners used in mechanical spray warewashing machines can be liquid, granular or solid in form. These high performance cleaners commonly contain active cleaning agents such as alkaline ingredients including alkali metal hydroxide, phosphates, silicates, chlorine yielding compounds, defoamers and organic threshold or chelating agents. See, for example, the disclosures of Mizuno et al, U.S. Pat. No. 3,166,513; Sabatelli et al, U.S. Pat. No. 3,535,285; Sabatelli et al, U.S. Pat. No. 3,579,455; Mizuno et al, U.S. Pat. No. 3,700,599; and Copeland et al, U.S. Pat. No. 3,899,436 for a discussion of such high performance cleaners.
The active-halogen or halogen oxidant bleach compositions can be present in the alkaline cleaners or can be separately added with the alkaline cleaner to provide a bleaching sanitizing effect during a cleaning cycle. The use of active halogen compositions in high performance cleaners in the cleaning cycle suffers from certain drawbacks. First, the active halogen compositions often interact with the components of the highly alkaline cleaners, reducing the effective concentration of active-halogen and the halogen-reactive cleaner components. Second, the pH of solutions containing the cleaning agents reduces the effectiveness of the active halogen composition. In a chlorine based halogen bleach, the active agent is commonly hypochlorous acid (HOCl). In an aqueous system the dissociation of hypochlorous acid is a function of pH. For example at pH 8, 21% of the hypochlorous acid is undissociated whereas at pH 11 about 0.03% is unassociated. At equal concentration of the source of halogen at pH 8 there is nearly 700 times as much hypochlorous acid available to bleach stains and sanitize surfaces than is available at pH 11. Third, in the cleaning cycle a majority of the halogen is consumed in non-stain removing or non-sanitizing reactions. A substantial excess of the active halogen composition is commonly present in the cleaning composition since the active halogen comes in contact with a large concentration of readily oxidizable organic materials which can rapidly react with halogen and reduce the concentration of active halogen. A large excess of active halogen composition is used to insure that at least some active halogen remains in the cleaner solution to destain and sanitize the tableware after the majority of the active halogen compound interacts with and is absorbed or reduced by organic soil. The use of substantial quantities of active halogen composition in the cleaner is an uneconomic waste of the chemical. Clearly, a clear economic and operation benefit can result from the removal of relatively large amounts of active halogen compositions from the cleaning compositions added to the wash cycle.
In view of the above, combining a rinse agent with an active halogen in a rinse cycle would prevent problems that arise during the use of active halogen compound in the cleaner solutions. One option involves separately metering the rinse agent and active halogen composition into the rinse cycle of the warewashing machine. However, this would result in an uneconomic duplication of metering systems. Accordingly, for economic and practical reasons a substantial need exists for a rinse composition which combines a rinse agent and an active halogen composition.
Rinse agents or sheeting agents are low foaming compounds commonly added to rinse water to produce a rinsing or sheeting action, to insure substantial rinse water removal and to aid in the prevention of spotting. The precise mechanism through which rinse agents cause the rinse water to form continuous sheets of water which drain cleanly from the surface is unknown. Commonly available commercial rinse agents typically comprise a low foaming surface active agent made from homopolymers or copolymers of an alkylene oxide such as ethylene oxide or propylene oxide or mixtures thereof. Typically the surfactants are formed by reacting an alcohol, a glycol, a carboxylic acid, an amine or a substituted phenol with various proportions and combinations of ethylene oxide and propylene oxide to form both random and block copolymer substituents. Rinse agents containing substituents formed from an alkyleneoxide are particularly sensitive to rapid degradation in the presence of active halogen compounds. Accordingly, the combination of active halogen with the majority of presently available commercial rinse compositions in the rinse cycle would result in degradation of both rinse agent and active halogen.
Rinse agents and other components of rinse compositions desirably have certain characteristics. The rinse agent must be soluble in an aqueous solution of active halogen composition. The rinse agent must not cause the consumption or degradation of more than about 25 wt-% and preferably less than 10 wt-% of the original active halogen composition. The active halogen must not in turn degrade the rinse agent. Further, the rinse agent compositions must produce a substantial and complete sheeting effect in the final rinse. The rinse composition must be substantially resistant to the production of large amounts of foam. Foaming is a substantial drawback in machine spray washers using a pump that transfers rinse solution from the reservoir to the spray mechanism. The pumps used in the machines are designed to efficiently move water which is substantially noncompressable, but cannot move foam which is substantially highly compressable air. In the presence of foam, the delivery of rinse water can be prevented, and in extreme cases the presence can result in damage to the pump.